Earth-boring metal matrix rotary drill bit

ABSTRACT

An earth-boring rotary drill bit includes a bit body, with a first region configured to carry a plurality of cutters for engaging a subterranean earth formation of a first particle-matrix composite material and a second region configured for attachment to a drill string of a second particle-matrix composite material having a second material composition, and an annular shank extending from the second region. Each of the first particle-matrix composite material and second particle-matrix composite material has a cast microstructure. A method of making an earth-boring rotary drill bit includes providing a plurality of hard particles in a mold to define a particle precursor; infiltrating the particle precursor sequentially with a plurality of molten matrix materials to form a corresponding plurality of layers, each comprising a particle-matrix mixture; and cooling the plurality of particle-matrix mixtures to solidify the matrix materials and form the bit body.

RELATED APPLICATIONS

This patent application claims priority to U.S. Provisional Patent Application Ser. No. 61/090,767, filed Aug. 21, 2008 which is incorporated herein by reference in its entirety.

BACKGROUND

Rotary drill bits are commonly used for subterranean drilling of bore holes or wells. Many types of drills and associated methods have been employed for such drilling. A common type of drilling employs a rotary drill bit affixed to the end of a drill string. Many types of rotary drill bits are used, including a fixed-cutter bit (often referred to as a “drag” bit), which typically includes a plurality of cutting elements secured to a face region of a bit body. The drill string includes tubular pipe and equipment segments that couple the drill bit located at the bottom of the borehole to other drilling equipment at the surface. A rotary table or top drive may be used for rotating the drill string and the drill bit within the borehole. Alternatively, the shank of the drill bit may be coupled directly to the drive shaft of a down-hole motor, which then may be used to rotate the drill bit.

Fixed-cutter type drill bits generally have either a disk shape or a substantially cylindrical shape, particularly on the cutting end that houses the cutting elements. The cutting elements each have a cutting surface that is generally made from a hard, super-abrasive material, such as polycrystalline diamond, often in the form of a substantially circular end surface of the element, and are often referred to as “polycrystalline diamond compact” (PDC) cutters. Many forms of such bits are possible; however, the cutting elements are often fabricated separately from the bit body and then fixed into pockets formed in its outer surface. The cutting elements may be fixed in any suitable manner, such as, for example, by use of a bonding material, including various adhesives or, more typically, various braze alloys. The bit body is secured to a hardened steel shank having an American Petroleum Institute (API) thread connection for attaching the drill bit to the drill string. In use, the cutting elements and their cutting surfaces are placed in contact with the earth formation to be drilled. As the bit is rotated, the cutting elements progressively shear away the surface of the underlying formation to form the borehole.

The bit body of a rotary drill bit may be formed from steel; however, such bit bodies experience abrasive wear, the rate of which can vary significantly as a function of the drilling environment. In order to reduce the wear and extend their life, bit bodies have also been made from particle-matrix composite materials.

Particle-matrix composite bit bodies have been fabricated in graphite molds with machined cavities. Additional fine features may be added to the cavity of the graphite mold by hand-held tools. Inserts or cores made from sand, clay or other materials may also be used to obtain the desired configuration of some features of the bit body. Where necessary, preform elements or displacements (which may be made from any suitable material, including ceramic components, graphite components, or resin-coated sand compact components) may be positioned within the mold and used to define various features, including internal passages, cutting element pockets, junk slots, and other external topographic or internal features of the bit body. The cavity of the graphite mold is filled with hard particulate carbide material (such as tungsten carbides, titanium carbides, tantalum carbides, etc.). The preformed steel blank is then positioned in the mold at the appropriate location and orientation, which typically is at least partially submerged in the particulate carbide material within the mold.

The mold then may be vibrated or the particles otherwise packed to increase the packing density of the carbide powder and produce the powder form. A matrix material, such as a copper-based alloy, is melted and introduced to the carbide powder so as to cause infiltration of the powder form by the molten matrix material. The mold and bit body are allowed to cool to solidify the matrix material and bond the steel blank to the particle-matrix composite material forming a crown. The mold and any displacements are removed from the bit body. Destruction of the graphite mold typically is required to remove the bit body.

After the bit body has been removed from the mold, the bit body may be secured to the steel shank. Thread forms may be machined on an exposed surface of the steel blank to provide a threaded connection between the bit body and the steel shank. Once the steel shank is threaded onto the bit body, a weld may then be provided along the interface between the bit body and the steel shank.

While steel blanks afford a generally acceptable means of connecting the steel shank and the bit body, shifting of the blank in the mold during infiltration can occur resulting in misalignment of the blank with respect to the bit body, thereby causing the bit body to be unusable, or requiring additional machining or other rework of the bit body. Further, introduction of the blank as an additional component requires that it be degreased or otherwise cleaned prior to infiltration to ensure a metallurgical bond between the blank and the metal matrix. Still further, depending on the material used for the blank, interaction between the blank and matrix material may lead to the formation of phases at the interface between them that can result in crack formation and propagation during use of the bit.

While bit bodies that include particle-matrix composite materials offer significant advantages over all-steel bit bodies in terms of abrasion and erosion-resistance, the lower strength and toughness of such bit bodies limit their use in certain applications. Improvement of the particle-matrix composite to increase the toughness, strength or other properties would increase the applications where such bit bodies may be used.

SUMMARY

In general terms, a rotary drill bit having a bit body that includes a plurality of particle-matrix composite layers with cast microstructures and an attached shank is disclosed. The bit body may be employed to improve the incorporation of a metal blank or shank into the bit body to reduce the possibility of misalignment or of not forming the necessary metallurgical bond or of forming undesirable phases at the interfaces between the bit body and these components. The bit body may also be employed to improve the toughness, strength or other properties of the particle-matrix composite and expand the number and types of applications in which they may be used, or extend their operating lifetimes.

In one aspect, an earth-boring rotary drill bit includes a bit body, with a first region configured to carry a plurality of cutters for engaging a subterranean earth formation of a first particle-matrix composite material and a second region configured for attachment to a drill string of a second particle-matrix composite material having a second material composition, and an annular shank extending from the second region. Each of the first particle-matrix composite material and second particle-matrix composite material has a cast microstructure.

In another aspect, an earth-boring rotary drill bit includes a bit body having a first region configured to carry one or more cutters for engaging a subterranean earth formation, the first region comprising a first particle-matrix composite material having a first material composition; and a second region configured for attachment to a drill string, the second region comprising a second particle-matrix composite material having a second material composition differing from the first material composition. Each of the first particle-matrix composite material and second particle-matrix composite material is substantially formed of a plurality of hard particles dispersed throughout a matrix material, wherein the matrix of the first particle-matrix composite and the matrix of the second particle-matrix composite each have a cast microstructure.

In yet another aspect, an earth-rotary drill bit includes a bit body having a first region configured to carry one or more cutters for engaging a subterranean earth formation, the first region comprising a first particle-matrix composite material having a first material composition, and a plurality of regions configured for attachment to a drill string, the plurality of regions comprising a corresponding plurality of particle-matrix composite materials having a corresponding plurality of material compositions differing from the first material composition. Each of the first particle-matrix composite materials and plurality of additional particle-matrix composite materials is substantially formed of a plurality of hard particles dispersed throughout a matrix material, wherein the matrix of the first particle-matrix composite and the plurality of additional particle-matrix composites each have a cast microstructure. A shank extends from at least one of the plurality of regions, the shank comprising an attachment portion configured to attach the shank to a drill string and a bit body portion for attaching the shank to a bit body.

BRIEF DESCRIPTION OF THE DRAWINGS

The following is a brief description of the drawings:

FIG. 1 is a schematic partial cross-sectional view of an exemplary embodiment of an earth-boring rotary drill bit disclosed herein;

FIG. 2 is a schematic partial cross-sectional view of a second exemplary embodiment of an earth-boring rotary drill bit disclosed herein;

FIG. 3 is a schematic partial cross-sectional view of a third exemplary embodiment of an earth-boring rotary drill bit disclosed herein;

FIG. 4 is a schematic partial cross-sectional view of a fourth exemplary embodiment of an earth-boring rotary drill bit disclosed herein;

FIG. 5 is a schematic partial cross-sectional view of a fifth exemplary embodiment of an earth-boring rotary drill bit disclosed herein; and

FIGS. 6A-F are schematic partial cross-sectional views illustrating a method of making an earth-boring rotary drill bit disclosed herein.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The illustrations presented herein, are not meant to be actual views of any particular material, apparatus, system, or method, but are merely idealized representations of that which is disclosed herein. Additionally, elements common between figures may retain the same numerical designation.

As used herein, the term “[metal]-based alloy” (where [metal] is any metal) means commercially pure [metal] in addition to metal alloys wherein the weight percentage of [metal] in the alloy is greater than the weight percentage of any other component of the alloy. Where two or more metals are listed in this manner, the weight percentage of the listed metals in combination is greater than the weight percentage of any other component of the alloy.

As used herein, the term “material composition” means the chemical composition and microstructure of a material. In other words, materials having the same chemical composition but a different microstructure are considered to have different material compositions.

As used herein, the term “tungsten carbide” means any material composition that contains chemical compounds of tungsten and carbon in any stoichiometric or non-stoichiometric ratio or proportion, such as, for example, WC, W₂C, and combinations of WC and W₂C. Tungsten carbide includes any morphological form of this material, for example, cast tungsten carbide, sintered tungsten carbide, and macrocrystalline tungsten carbide.

An exemplary embodiment of an earth-boring rotary drill bit 10 having a bit body that includes a multi-layer particle-matrix composite material is illustrated in FIG. 1. The bit body 12 is secured to a shank 20, such as a steel shank. The bit body 12 includes a crown or first region 14, a body portion or second region 15 and a steel blank 16 that is partially embedded in the crown 14 and body portion 15. The crown 14 includes a first particle-matrix composite material such as, for example, particles of tungsten carbide embedded in a copper alloy matrix material.

The body portion 15 includes a second particle-matrix composite material such as, for example, particles of tungsten carbide embedded in an iron-base alloy matrix material, such as steel. The first particle-matrix composite material has a first material composition and the second particle-matrix composite material has a second material composition, wherein the first material composition and the second material composition are different material compositions. Many other material compositions are possible for both crown 14 and body portion 15 and any suitable combination of particles and matrix materials may be used. The particle-matrix composite material of the first region 14 may include a plurality of hard particles dispersed randomly throughout a matrix material. The hard particles may comprise diamond or ceramic materials such as carbides, nitrides, oxides, and borides (including boron carbide (B₄C)) and combinations of them, such as carbonitrides. More specifically, the hard particles may comprise carbides and borides made from elements such as W, Ti, Mo, Nb, V, Hf, Ta, Cr, Zr, Al, and Si. By way of example and not limitation, materials that may be used to form hard particles include tungsten carbide (WC, W₂C), titanium carbide (TiC), tantalum carbide (TaC), titanium diboride (TiB₂), chromium carbides, titanium nitride (TiN), vanadium carbide (VC), aluminium oxide (Al₂O₃), aluminium nitride (AlN), boron nitride (BN), and silicon carbide (SiC). Furthermore, combinations of different hard particles may be used to tailor the physical properties and characteristics of the particle-matrix composite material. The hard particles may be formed using techniques known to those of ordinary skill in the art. Most suitable materials for hard particles are commercially available and the formation of the remainder is within the ability of one of ordinary skill in the art.

The matrix material of the particle-matrix composite material may include, for example, cobalt-based, iron-based, nickel-based, iron and nickel-based, cobalt and nickel-based, iron and cobalt-based, aluminum-based, copper-based, magnesium-based, and titanium-based alloys. The matrix material may also be selected from commercially pure elements such as cobalt, aluminum, copper, magnesium, titanium, iron, and nickel. By way of example and not limitation, the matrix material may include carbon steel, alloy steel, stainless steel, tool steel, Hadfield manganese steel, nickel or cobalt superalloy material, and low thermal expansion iron or nickel based alloys such as INVAR®. As used herein, the term “superalloy” refers to an iron, nickel, and cobalt based-alloys having at least 12% chromium by weight. Additional exemplary alloys that may be used as matrix material include austenitic steels, nickel based superalloys such as INCONEL® 625M or Rene 95, and INVAR® type alloys having a coefficient of thermal expansion that closely matches that of the hard particles used in the particular particle-matrix composite material. More closely matching the coefficient of thermal expansion of matrix material with that of the hard particles offers advantages such as reducing problems associated with residual stresses and thermal fatigue. Another exemplary matrix material is a Hadfield austenitic manganese steel (Fe with approximately 12% Mn by weight and 1.1% C by weight).

The material composition of the second region 15 of the bit body may include, for example, any of the previously described matrix materials of the particle-matrix composite material used for the first region 14 of the bit body 12. Alternatively, the material composition of the second region 15 of the bit body 12 may include a particle-matrix composite material in which hard particles are randomly dispersed throughout a matrix material. The hard particles and the matrix materials may be selected from those previously described in relation to the first region 14 of the bit body 12, other than the combination selected for first region 14. The material composition of the second region 15 of the bit body 12, however, may be selected to facilitate machining of the second region 15 using conventional machining techniques. Such conventional machining techniques may include, for example, turning, milling, and drilling techniques, which may be used to configure the second region 15 of the bit body 12 for attachment to the shank 20. Exemplary combinations of matrix materials include the use of Cu-based alloys as the first material composition in the crown 14 Ni-based alloys in the second material composition in body portion 15. Another exemplary combination includes the use of Fe-based alloys as the first material composition in crown 14 and Cu-based alloys as the second material composition in body portion 15. Yet another exemplary combination includes the use of Cu-based alloys as the first material composition in crown 14 and Fe-based alloys as the second material composition in body portion 15. The layers of particle-matrix composite materials will have a cast microstructure which will include one or more of dendrites in one or more of the matrix materials or interface layers between the matrix materials, various inclusions or other impurities generally associated with a casting process, porosity associated with the casting process or subsequent solidification of the matrix materials, or other aspects of the composition or morphology of the matrix materials or hard particles. For example, the existence of a cast tungsten carbide having the cast morphology and composition W₂C, which is metastable and desirable for use because of its higher hardness relative to the more stable WC and thus used in relatively larger particle sizes, and suitable for use in an infiltration process because of the generally shorter times at high temperature prior to solidification and cooling of the matrix material (in contrast with other methods of making a particle-matrix composite materials such as various powder metallurgy processes that typically employ much longer times at high sintering temperatures.

The bit body 12 is secured to the steel shank 20 by way of a threaded connection 22 and a weld 24 extending around the drill bit 10 on an exterior surface thereof along an interface between the bit body 12 and the steel shank 20. The steel shank 20 includes an API threaded connection portion 28 for attaching the drill bit 10 to a drill string (not shown).

The bit body 12 includes wings or blades 30, which are separated by external channels or conduits also known as junk slots 32. Internal fluid passageways 42 extend between the face 18 of the bit body 12 and a longitudinal bore 40, which extends through the steel shank 20 and partially through the bit body 12. Nozzle inserts (not shown) may be provided at face 18 of the bit body 12 within the internal fluid passageways 42.

A plurality of PDC cutters 34 may be provided on the face 18 of the bit body 12. The PDC cutters 34 may be provided along the blades 30 within pockets 36 formed in the face 18 of the bit body 12, and may be supported from behind by buttresses 38, which may be integrally formed with the crown 14 of the bit body 12.

The steel blank 16 shown in FIG. 1 is generally cylindrically tubular. Alternatively, the steel blank 16 may have a fairly complex configuration and may include external protrusions corresponding to blades 30 or other features on and extending on the face 18 of the bit body 12 (not shown), or a plurality of annually spaced slots which facilitate continuity of the first particle-matrix composite material and the second particle-matrix composite material between an inner surface 17 and outer surface 19 of steel blank 16.

During drilling operations, the drill bit 10 is positioned at the bottom of a wellbore and rotated while drilling fluid is pumped to the face 18 of the bit body 12 through the longitudinal bore 40 and the internal fluid passageways 42. As the PDC cutters 34 shear or scrape away the underlying earth formation, the formation cuttings mix with and are suspended within the drilling fluid and pass through the junk slots 32 and the annular space between the wellbore and the drill string to the surface of the earth formation.

A method of making earth boring rotary drill bits having multi-layer particle-matrix composite bit bodies of the type described herein is described in FIGS. 6A-6F. Referring to FIG. 6A, bit bodies that include a multi-layer particle-matrix composite material, such as those described herein may be fabricated in graphite molds 100. The cavities 102 of the graphite molds may be conventionally machined with a five-axis machine tool. Fine features may then be added to the cavity of the graphite mold by hand-held tools. Additional clay work may also be required to obtain the desired configuration of some features of the bit body. Where necessary, preform elements or displacements 104 (which may include ceramic components, graphite components, resin-coated sand compact components and the like) may be positioned within the mold and used to define the internal passageways 42, cutting element pockets 36, junk slots 32, and other external topographic features of the bit body.

The cavity 102 of the graphite mold is filled, as shown by arrow P, with hard particulate material 106 of the types described herein as shown in FIG. 6B. This may include particulate material with the single range of sizes, or a single material with a plurality of size ranges along the depth of cavity 102 (i.e., along its longitudinal axis 108). The hard particles may also comprise a plurality of different hard particle materials. For example, the hard particles may have a first hard particle composition, size distribution or both in the first region of the mold 110 and a different hard particle composition, size distribution or both in the second region 112. Further, the hard particles may include more than two hard particle compositions, size distributions, or both, in any number. Once loaded into the mold cavity 102, hard particles 106 may be compacted or otherwise densified, such as by vibrating the mold, to decrease the amount of space between adjacent particles of the particulate material and form particle precursor 114 that will be infiltrated by the respective matrix materials in the manner described herein. An insert, such as preformed steel blank 16 may then be positioned in the mold at the appropriate location and orientation. A steel blank 16 typically is at least partially embedded in the particulate material within the mold.

A first matrix material, such as a copper-based alloy, is melted and poured into the mold cavity as illustrated by arrow M1. The particulate precursor 114 is infiltrated with the first molten matrix material M1 to form a first molten particle-matrix material mixture 116. The mold and bit body 12 may be cooled to solidify the first matrix material and form the first particle-matrix composite in the first region 110. In another exemplary embodiment, the process may also proceed without solidification of the matrix material. Whether or not to solidify the first matrix material prior to infiltration of a second matrix material will depend upon factors such as the relative melting points, densities, the desired microstructure of the bit body, including the interface layers formed between the particle-matrix composite layers, and the like. It is desirable that mixing of the first matrix material and any subsequent matrix materials be controlled and limited so as to avoid the complete intermixing of the matrix materials and maintain separate layers of the respective matrix materials; however, a randomly intermixed structure of the matrix materials may also be employed. In FIG. 6C, the first particle-matrix material mixture 116 is illustrated as being in a molten state just prior to infiltration of the subsequent matrix layer. The second matrix layer (M2) is melted and poured into the mold so as to infiltrate the particle precursor 114 in the second region with a molten second matrix material, thereby forming a molten second particle-matrix material 118 mixture. The hard particle precursor 112 may extend part way or fully into the second region of the mold. As discussed above with respect to the first matrix material, the second matrix material may be solidified prior to any further infiltration or casting into the mold, or such casting or infiltration may be performed prior to solidification of the second matrix material or first matrix material or both of them. Casting is used herein to designate addition of a molten matrix material into a portion of the mold cavity that does not include particle precursor 112, but with respect to the addition of a molten material to the mold cavity generally, the terms may be used interchangeably. Similar to considerations described above with respect to the first matrix material, whether the second matrix material is solidified prior to any subsequent infiltration or casting is determined using the same criteria as described above with respect to the first matrix material; however, the design considerations are with respect to the second matrix material and any other matrix materials which are subsequently added to the mold. As illustrated in FIG. 6D and FIG. 6E, both the first matrix material and second matrix material are illustrated as being still molten upon addition of a molten third matrix material (M3) 120. The third matrix material may be a metal alloy as illustrated in FIG. 6E, or may also include hard particles in the melt which is poured into the mold. Further, the hard particle precursor 112 may also extend part way or fully into the third region of the mold (not shown). Where the third region comprises a metal shank, such as a steel shank, as shown in FIG. 5, it may be desirable that the material cast into the third region be a metal alloy, such as an Fe-based alloy, including various grades of steel. Referring to FIGS. 6E and 6F, upon filling the mold, the bit body 12, including any integrally formed shank, is cooled to solidify the matrix materials and form a multi-layer particle matrix composite having a first particle-matrix material layer 122, second particle-matrix material layer 124 and third particle-matrix material layer 126. The embodiment used to illustrate the method is most similar to the drill bit illustrated in FIG. 5, but is equally applicable with adjustment of the number of layers employed to all of the bit configurations illustrated in FIGS. 1-5.

If the respective matrix materials are immiscible in their molten state, or have substantially no solid solubility in the solid state over the temperatures at which the drill bit is used, a relatively distinct boundary or interface between each of the respective matrix materials and particle-matrix materials will be expected with a cast microstructure as described herein. If, however, adjacent matrix materials have at least limited solubility, they will have an interface layer between them, such as first interface layer 122 or second interface layer 124, which includes one of the solid solution or a plurality of phases of the respective matrix constituents having a predetermined thickness and a cast microstructure. The predetermined thickness and cast microstructure will depend on many factors, including, without limitation, the relative melting temperatures, phase equilibrium characteristics of the constituents of adjacent matrix materials, the rate of cooling, whether the matrix material which was added to the mold first (and any subsequently added matrix material) was solidified prior to addition of the subsequent matrix material or materials, the cooling rate and direction during solidification of the interface layer, factors affecting nucleation of the matrix materials during solidification and other aspects of the matrix or particle materials. This being the case, the interface layers between the respective matrix materials may be controlled to provide desirable strength and toughness characteristics at these locations and avoid the development of brittle phases, porosity, or other microstructural features, which have a propensity to crack along the interface layers.

Referring again to FIG. 1, the mold may also include an insert, such as steel blank 16 upon solidification, the steel blank 16 is bonded to at least one or more of the particle-matrix composite materials forming the crown 14 or body portion 15 upon cooling of the bit body 12 and solidification of the matrix material. Once the bit body 12 has cooled, the bit body 12 is removed from the mold and any displacements are removed from the bit body 12. Destruction of the graphite mold may be required to remove the bit body 12.

After the bit body 12 has been removed from the mold and any secondary operations desired to form the bit body 12 or steel blank 16 have been employed, such as machining or grinding, the bit body 12 may be secured to the steel shank 20. As the particle-matrix composite material used to form the crown 14 is relatively hard and not easily machined, the steel blank 16 is used to secure the bit body to the shank. Threads may be machined on an exposed surface of the steel blank 16 to provide a threaded connection 22 between the bit body 12 and the steel shank 20. The steel shank 20 may be screwed onto the bit body 12, and a weld 24 then may be provided along the interface between the bit body 12 and the steel shank 20.

The PDC cutters 34 may be bonded to the face 18 of the bit body 12 after the bit body 12 has been cast by, for example, brazing, mechanical, or adhesive affixation. Alternatively, the cutters 34 may be bonded to the face 18 of the bit body 12 during forming of the bit body 12 if thermally stable synthetic or natural diamonds are employed in the cutters 34.

An earth-boring rotary drill bit 50 of a second exemplary embodiment of the present invention is shown in FIG. 2. The rotary drill bit 50 has a bit body 52 that includes a two-layer particle-matrix composite material. The rotary drill bit 50 may also include a shank 70 attached to the bit body 52.

The shank 70 includes a generally cylindrical outer wall having an outer surface and an inner surface. The outer wall of the shank 70 encloses at least a portion of a longitudinal bore 66 that extends through the rotary drill bit 50. At least one surface of the outer wall of the shank 70 may be configured for attachment of the shank 70 to the bit body 52. The shank 70 also may include a male or female API threaded connection portion 28 for attaching the rotary drill bit 50 to a drill string (not shown). One or more apertures 72 may extend through the outer wall of the shank 70. These apertures are described in greater detail below.

The bit body 52 of the rotary drill bit 50 is formed from and composed of a two-layer particle-matrix composite material as described herein. Furthermore, the composition of the particle-matrix composite material is selectively varied within the bit body 52 to provide various regions within the bit body that have different, custom tailored physical properties or characteristics.

By way of example and not limitation, the bit body 52 may include first region 54 having a first material composition and a body portion or second region 56 having a second material composition that is different from the first material composition. The first region 54 may include the longitudinally-lower and laterally-outward regions of the bit body 52. The first region 54 may include the face 68 of the bit body 52, which may be configured to carry a plurality of cutting elements, such as PDC cutters 34. For example, a plurality of pockets 36 and buttresses 38 may be provided in or on the face 68 of the bit body 52 for carrying and supporting the PDC cutters 34. Furthermore, a plurality of blades 30 and junk slots 32 maybe provided in the first region 54 of the bit body 52. The body portion or second region 56 may include the longitudinally-upper and laterally-inward regions of the bit body 52. The longitudinal bore 66 may extend at least partially through the second region 56 of the bit body 52.

The second region 56 may include at least one surface 58 that is configured for attachment of the bit body 52 to the shank 70. By way of example and not limitation, at least one groove 60 may be formed in at least one surface 58 of the second region 56 that is configured for attachment of the bit body 52 to the shank 70. Each groove may correspond to and be aligned with an aperture extending through the outer wall of the shank 70. A retaining member 80 may be provided within each aperture in the shank 70 and each groove 60. Either mechanical interference, a weld joint or braze joint, or a combination of them between the shank 70, the retaining member 80, and the bit body 52 may prevent longitudinal separation of the bit body 52 from the shank 70, and may prevent rotation of the bit body 52 about a longitudinal axis L₅₀ of the rotary drill bit 50 relative to the shank 70.

In the embodiment shown in FIG. 2, the rotary drill bit 50 includes two retaining members 80. By way of example and not limitation, each retaining member 80 may include an elongated, cylindrical rod or pin that extends through an aperture in the shank 70 and a groove 60 formed in a surface 58 of the bit body 52.

The mechanical interference between the shank 70, the retaining member 80, and the bit body 52 may also provide a substantially uniform clearance or gap between a surface of the shank 70 and the surfaces 58 in the second region 56 of the bit body 52. By way of example and not limitation, a substantially uniform gap of between about 50 microns (0.002 inches) and about 150 microns (0.006 inches) may be provided between the shank 70 and the bit body 52 when the retaining members 80 are disposed within the apertures in the shank 70 and the grooves 60 in the bit body 52.

A brazing material 82 such as, for example, a silver-based or nickel-based metal alloy may be provided in the substantially uniform gap between the shank 70 and the surfaces 58 in the second region 56 of the bit body 52. As an alternative to brazing, or in addition to brazing, a weld 24 may be provided around the rotary drill bit 50 on an exterior surface thereof along an interface between the bit body 52 and the steel shank 70. The weld 24 and the brazing material 82 may be used to further secure the shank 70 to the bit body 52. In this configuration, if the brazing material 82 in the substantially uniform gap between the shank 70 and the surfaces 58 in the second region 56 of the bit body 52 and the weld 24 should fail while the rotary drill bit 50 is located at the bottom of a well bore-hole during a drilling operation, the retaining members 80 may prevent longitudinal separation of the bit body 52 from the shank 70, thereby preventing loss of the bit body 52 in the well bore-hole.

As previously stated, the first region 54 of the bit body 52 has a first material composition and the second region 56 of the bit body 52 has a second material composition that is different from the first material composition. The first region 54 may include a particle-matrix composite material. The second region 56 of the bit body 52 may include a metal, a metal alloy, or a particle-matrix composite material. By way of example and not limitation, the material composition of the first region 54 may be selected to exhibit higher erosion and wear-resistance than the material composition of the second region 56. The material composition of the second region 56 may be selected to facilitate machining of the second region 56. The manner in which the physical properties may be tailored to facilitate machining of the second region 56 may be at least partially dependent of the method of machining that is to be used. For example, if it is desired to machine the second region 56 using conventional turning, milling, and drilling techniques, the material composition of the second region 56 may be selected to exhibit lower hardness and higher ductility. Alternatively, if it is desired to machine the second region 56 using ultrasonic machining techniques, which may include the use of ultrasonically-induced vibrations delivered to a tool, the composition of the second region 56 maybe selected to exhibit a higher hardness and a lower ductility. In some embodiments, the material composition of the second region 56 may be selected to exhibit higher fracture toughness than the material composition of the first region 54. In yet other embodiments, the material composition of the second region 56 may be selected to exhibit physical properties that are tailored to facilitate welding of the second region 56. By way of example and not limitation, the material composition of the second region 56 may be selected to facilitate welding of the second region 56 to the shank 70. It is understood that the various regions of the bit body 52 may have material compositions that are selected or tailored to exhibit any desired particular physical property or characteristic, and the present invention is not limited to selecting or tailing the material compositions of the regions to exhibit the particular physical properties or characteristics described herein.

Certain physical properties and characteristics of a composite material (such as hardness) may be defined using an appropriate rule of mixtures, as is known in the art. Other physical properties and characteristics of a composite material may be determined without resort to the rule of mixtures. Such physical properties may include, for example, erosion and wear resistance.

The particle-matrix composite material of the first region 54 may include a plurality of hard particles dispersed randomly throughout a matrix material as described herein.

The material composition of the second region 56 of the bit body may include, for example, any of the previously described matrix materials of the particle-matrix composite material used for the first region 54 of the bit body 52. Alternatively, the material composition of the second region 56 of the bit body 52 may include a particle-matrix composite material in which hard particles are randomly dispersed throughout a matrix material. The hard particles and the matrix materials may be selected from those previously described in relation to the first region 54 of the bit body 52, other than the combination selected for first region 54. The material composition of the second region 56 of the bit body 52, however, may be selected to facilitate machining of the second region 56 using conventional machining techniques. Such conventional machining techniques may include, for example, turning, milling, and drilling techniques, which may be used to configure the second region 56 of the bit body 52 for attachment to the shank 70. For example, features such as the grooves 60 may be machined in one or more surfaces 58 of the second region 56 of the bit body 52 to configure the second region 56 of the bit body 52 for attachment to the shank 70.

The second region 56 of the bit body 52 may be substantially formed from and composed of the same material used as matrix material in the particle-matrix composite material of the first region 54.

In another embodiment, both the first region 54 and the second region 56 of the bit body 52 may be substantially formed from and composed of a particle-matrix composite material.

The matrix material of the second region 56 maybe substantially identical to the matrix material of the particle-matrix composite material of the first region 54. Alternatively, the matrix material of the particle-matrix composite material of the second region 56 may differ from the matrix material of the particle-matrix composite material of the first region 54.

The methods of forming earth-boring rotary drill bits described herein may allow the formation of novel drill bits having bit bodies that include particle-matrix composite materials that exhibit superior erosion and wear-resistance, strength, and fracture toughness relative to known particle-matrix composite drill bits. The methods allow for attachment of the shank to the bit body with proper alignment and concentricity provided therebetween. The methods described herein allow for improved attachment of a shank to a bit body having at least a crown region that includes a particle-matrix composite material by precision machining at least a surface of the bit body, the surface being configured for attachment of the bit body to the shank.

With continued reference to FIG. 2, the shank 70 includes a male or female API threaded connection portion for connecting the rotary drill bit 50 to a drill string (not shown). The shank 70 may be formed from and composed of a material that is relatively tough and ductile relative to the bit body 52. By way of example and not limitation, the shank 70 may include a steel alloy.

As the particle-matrix composite material of the bit body 52 maybe relatively wear-resistant and abrasive, machining of the bit body 52 may be difficult or impractical. As a result, conventional methods for attaching the shank 70 to the bit body 52, such as by machining cooperating positioning threads on mating surfaces of the bit body 52 and the shank 70, with subsequent formation of a weld 24, may not be feasible or desirable.

As an alternative to conventional methods for attaching the shank 70 to the bit body 52, the bit body 52 may be attached and secured to the shank 70 by brazing or soldering an interface between abutting surfaces of the bit body 52 and the shank 70. By way of example and not limitation, a brazing alloy 74 may be provided at an interface between a surface 58 of the bit body 52 and a surface 84 of the shank 70. Furthermore, the bit body 52 and the shank 70 may be sized and configured to provide a predetermined stand off between the surface 58 and the surface 84, in which the brazing alloy 74 may be provided.

Furthermore, interfering non-planar surface features may be formed on the surface 58 of the bit body 52 and the surface 84 of the shank 70. For example, threads or longitudinally-extending splines, rods, or keys (not shown) may be provided in or on the surface 58 of the bit body 52 and the surface 84 of the shank 70 to prevent rotation of the bit body 52 relative to the shank 70.

During all infiltration or casting processes, refractory structures or displacements (not shown) may be used to support at least portions of the bit body and maintain desired shapes and dimensions during the solidification process. Such displacements may be used, for example, to maintain consistency in the size and geometry of the cutter pockets 36 and the internal fluid passageways 42 during the sintering process. Such refractory structures may be formed from, for example, graphite, silica, or alumina. The use of alumina displacements instead of graphite displacements may be desirable as alumina may be relatively less reactive than graphite, thereby minimizing atomic diffusion during solidification. Additionally, coatings such as alumina, boron nitride, aluminum nitride, or other commercially available materials may be applied to the refractory structures to prevent carbon or other atoms in the refractory structures from diffusing into the bit body during solidification.

As previously discussed, several different methods may be used to attach the shank 70 to the bit body 52. In the embodiment shown in FIG. 2, the shank 70 may be attached to the bit body 52 by brazing or soldering the interface between the surface 58 of the bit body 52 and the surface 84 of the shank 70. The bit body 52 and the shank 70 may be sized and configured to provide a predetermined standoff between the surface 58 and the surface 84, in which the brazing alloy 74 may be provided. Furthermore, the brazing alloy 74 may be applied to the interface between the surface 58 of the bit body 52 and the surface 84 of the shank 70 using a furnace brazing process or a torch brazing process. The brazing alloy 74 may include, for example, a silver-based or a nickel-based alloy.

A shrink fit may also be provided between the shank 70 and the bit body 52 in alternative embodiments. By way of example and not limitation, the shank 70 may be heated to cause thermal expansion of the shank while the bit body 52 is cooled to cause thermal contraction of the bit body 52. The shank 70 then may be pressed onto the bit body 52 and the temperatures of the shank 70 and the bit body 52 may be allowed to equilibrate. As the temperatures of the shank 70 and the bit body 52 equilibrate, the surface 84 of the shank 70 may engage or abut against the surface 58 of the bit body 52, thereby at least partly securing the bit body 52 to the shank 70 and preventing separation of the bit body 52 from the shank 70.

In another alternative embodiment, a friction weld may be provided between the bit body 52 and the shank 70. Mating surfaces may be provided on the shank 70 and the bit body 52. A machine may be used to press the shank 70 against the bit body 52 while rotating the bit body 52 relative to the shank 70. Heat generated by friction between the shank 70 and the bit body 52 may at least partially melt the material at the mating surfaces of the shank 70 and the bit body 52. The relative rotation may be stopped and the bit body 52 and the shank 70 may be allowed to cool while maintaining axial compression between the bit body 52 and the shank 70, providing a friction welded interface between the mating surfaces of the shank 70 and the bit body 52.

In yet another alternate embodiment, commercially available adhesives such as, for example, epoxy materials (including inter-penetrating network (IPN) epoxies), polyester materials, cyanoacrylate materials, polyurethane materials, and polyimide materials may also be used to secure the shank 70 to the bit body 52.

A circumferential weld 24 may also be provided between the bit body 52 and the shank 70, separately or in combination with the welding, brazing and pin attachments described herein, that extends around the rotary drill bit 50 on an exterior surface thereof along an interface between the bit body 52 and the shank 70. A shielded metal arc welding (SMAW) process, a gas metal arc welding (GMAW) process, a plasma transferred arc (PTA) welding process, a submerged arc welding process, an electron beam welding process, or a laser beam welding process may be used to weld the interface between the bit body 52 and the shank 70. Furthermore, the interface between the bit body 52 and the shank 70 may be soldered or brazed using processes known in the art to further secure the bit body 52 to the shank 70.

FIG. 3 illustrates a third exemplary embodiment which is similar to that of FIG. 2, except that the bit body includes a third region 57 and the joint does not employ pins or rods to secure the bit body 52 to the shank 70. The third region 57 may include any of the metal matrices described herein without hard particles, or in an alternate embodiment, may incorporate a plurality of hard particles added to the melt used to cast this region, or alternately by infiltration of a particle precursor which extends into the third region of the bit body which in this instance includes an attachment portion, namely a protrusion from the bit body 52 that is adapted to be attached to the mating recess formed on the end of the shank 70 proximate the bit body 52. This embodiment is particularly adapted to employ the various welding, brazing, and adhesive joints described herein for attachment of the bit body and shank.

A fourth and fifth exemplary embodiment of an earth-boring rotary drill bit 150 having a multi-layer particle-matrix bit body are shown in FIGS. 4 and 5, respectively. The drill bit 150 includes a unitary structure 151 that includes a bit body 152,154 and an integrally formed shank 156. The unitary structure 151 is substantially formed from and composed of a multi-layer particle-matrix composite material as described herein. In this configuration, it may not be necessary to use a separate shank to attach the drill bit 150 to a drill string, as the shank 156 may be formed integrally with the unitary structure 151 using the method described herein.

The bit body 152,154 includes blades 30, which are separated by junk slots 32. Internal fluid passageways 42 extend between the face 158 of the bit body 152,154 and a longitudinal bore 40, which at least partially extends through the unitary structure 151. Nozzle inserts (not shown) maybe provided at face 158 of the bit body 152 within the internal fluid passageways 42.

The drill bit 150 may include a plurality of PDC cutters 34 disposed on the face 68 of the bit body 152, 154. The PDC cutters 34 may be provided along blades 30 within pockets 36 formed in the face 158 of the bit body 152, 154, and may be supported from behind by buttresses 38, which may be integrally formed with the of the bit body 152, 154. Alternatively, the drill bit 150 may include a plurality of cutters each comprising an abrasive, wear-resistant material such as, for example, cemented tungsten carbide.

The unitary structure 151 may include a plurality of regions. Each region may comprise a particle-matrix composite material having a material composition that differs from other regions of the plurality of regions. For example, the bit body 152, 154 may include a crown 152 of a first particle-matrix composite material having a first material composition, a body portion 154 of a second particle-matrix composite material having a second material composition and an integrally formed shank 156 of a third particle-matrix composite material having a third material composition. The material compositions of all three regions may be different as described elsewhere herein. Alternately, the matrix material of the second and third regions may be the same, and the particle precursor used to form the bit body in the manner described herein may be formed to fill the second region, while extending partially, fully or not at all into the third region. For example, in the embodiment of FIG. 4, the particle precursor generally does not extend into the third region, such that the shank 156 may be formed of metal alloy, such as steel, and extends along, and is integrally formed with and bonded to both the crown or first region 152 and body portion or second region 154. In another example, in the embodiment of FIG. 5, the particle precursor has a different configuration such that the shape of the second region is different, but the particle precursor still does not extend into the third region, such that the shank 156 may be formed of metal alloy, such as steel, that extends from, and is integrally formed with and bonded to, body portion 154.

The integral shank 156 may include a particle-matrix composite material having a third material composition that is different from the first material composition of the first region and second material composition of the second region. In this configuration, the material composition of the bit body 152,154 may exhibit a physical property that differs from the physical property exhibited by the material composition of the shank 156. For example, the first material composition, second material composition, or both of them, may exhibit higher erosion and wear resistance relative to the third material composition, and the third material composition may exhibit higher fracture toughness relative to the first material composition.

The drill bits 150 shown in FIGS. 4 and 5 include three distinct regions, each of which comprises a particle-matrix composite material having a unique material composition. In alternative embodiments, the drill bit 150 may include additional regions, each having a unique material composition. Furthermore, a discrete boundary is identifiable between each of the distinct regions of the drill bit 150 shown in FIGS. 4 and 5. In alternative embodiments, a continuous material composition gradient may be provided throughout the unitary structure 151 to provide a drill bit having a plurality of different regions, each having a unique material composition, but lacking any identifiable boundaries between the various regions. In this manner, the physical properties and characteristics of different regions within the drill bit 150 may be tailored to improve properties such as, for example, wear resistance, fracture toughness, strength, or weldability in strategic regions of the drill bit 150. It is understood that the various regions of the drill bit may have material compositions that are selected or tailored to exhibit any desired particular physical property or characteristic, and the present invention is not limited to selecting or tailing the material compositions of the regions to exhibit the particular physical properties or characteristics described herein.

While the description herein presents certain preferred embodiments, those of ordinary skill in the art will recognize and appreciate that it is not so limited. Rather, many additions, deletions and modifications to the preferred embodiments may be made without departing from the scope of the invention as hereinafter claimed. In addition, features from one embodiment may be combined with features of another embodiment while still being encompassed within the scope of the invention as contemplated by the inventors. Further, the invention has utility in drill bits and core bits having different and various bit profiles as well as cutter types.

The foregoing invention has been described in accordance with the relevant legal standards, thus the description is exemplary rather than limiting in nature. Variations and modifications to the disclosed embodiments may become apparent to those skilled in the art. Accordingly, the scope of legal protection afforded will be determined in accordance with the following claims. 

1. An earth-boring rotary drill bit comprising: a bit body having a first region configured to carry one or more cutters for engaging a subterranean earth formation, the first region comprising a first particle-matrix composite material having a first material composition; and a second region configured for attachment to a drill string, the second region comprising a second particle-matrix composite material having a second material composition differing from the first material composition, each of the first particle-matrix composite material and second particle-matrix composite material substantially formed of a plurality of hard particles dispersed throughout a matrix material, wherein the matrix of the first particle-matrix composite and the matrix of the second particle-matrix composite each have a cast microstructure; and a shank extending from the second region, the shank comprising an attachment portion configured to attach the shank to a drill string and a bit body portion for attaching the shank to the bit body.
 2. The rotary drill bit of claim 1, wherein the hard particles comprise diamond, or metal or semi-metal carbides, nitrides, oxides, or borides.
 3. The rotary drill bit of claim 1, wherein the matrix materials comprise cobalt-based alloys, iron-based alloys, nickel-based alloys, cobalt and nickel-based alloys, iron and nickel-based alloys, iron and cobalt-based alloys, aluminum-based alloys, copper-based alloys, magnesium-based alloys and titanium-based alloys.
 4. The rotary drill bit of claim 1, wherein the matrix of the first material composition has a first melting temperature and the matrix of the second material composition has a second melting temperature and the first melting temperature and second melting temperature are different.
 5. The rotary drill bit of claim 1, wherein the first melting point is lower than the second melting point.
 6. The rotary drill bit of claim 1, wherein the first melting point is higher than the second melting point.
 7. The rotary drill bit of claim 1, wherein the matrix of the first material composition comprises a Cu-based alloy and the matrix of the second material composition comprises a Ni-based alloy.
 8. The rotary drill bit of claim 1, wherein the matrix of the first material composition comprises a Fe-based alloy and the matrix of the second material composition comprises a Cu-based alloy.
 9. The rotary drill bit of claim 1, wherein the matrix of the first material composition comprises a Cu-based alloy and the matrix of the second material composition comprises a Fe-based alloy.
 10. The rotary drill bit of claim 1, further comprising a steel blank having a lower portion that is metallurgically bonded to the second region and an upper portion that is attached to the bit body portion of the shank.
 11. The rotary drill bit of claim 1, wherein the bit body portion of the shank has one of a recessed portion or a protruding portion and the second region has one of a protruding portion or a recessed portion, respectively, such that the recessed portion is configured to matingly engage and attach the protruding portion.
 12. The rotary drill bit of claim 9, wherein the recessed portion and the protruding portion are attached by at least one of a weld joint, braze joint, threaded joint, adhesive joint or pinned joint using one or more attachment pins, or any combination thereof.
 13. The rotary drill bit of claim 1, wherein the matrix of the first material composition and the matrix of the second material composition have substantially no solid solubility, and have an interface between them with substantially no interdiffusion of the matrix materials.
 14. The rotary drill bit of claim 1, wherein the matrix of the first material composition and the matrix of the second material composition have at least limited solid solubility, and have an interface between them comprising one of a solid solution or a plurality of phases of the respective matrices having a predetermined thickness and a cast microstructure.
 15. The rotary drill bit of claim 1, further comprising a third region extending from and integrally formed with the second region, wherein the third region comprises cobalt-based alloys, iron-based alloys, nickel-based alloys, cobalt and nickel-based alloys, iron and nickel-based alloys, iron and cobalt-based alloys, aluminum-based alloys, copper-based alloys, magnesium-based alloys and titanium-based alloys.
 16. The rotary drill bit of claim 15, further comprising a plurality of hard particles dispersed throughout the metal as a matrix, wherein the hard particles comprise diamond, or metal or semi-metal, nitrides, oxides, or borides, and wherein the metal and hard particles comprise a third particle-matrix composite.
 17. The rotary drill bit of claim 15, wherein the third region comprises the shank.
 18. The rotary drill bit of claim 1, wherein the cast microstructure of at least one of the matrix of the first particle-matrix composite and the matrix of the second particle-matrix composite comprises a plurality of dendrites.
 19. An earth-boring rotary drill bit comprising: a bit body having a first region configured to carry one or more cutters for engaging a subterranean earth formation, the first region comprising a first particle-matrix composite material having a first material composition; and a second region configured for attachment to a drill string, the second region comprising a second particle-matrix composite material having a second material composition differing from the first material composition, each of the first particle-matrix composite material and second particle-matrix composite material substantially formed of a plurality of hard particles dispersed throughout a matrix material, wherein the matrix of the first particle-matrix composite and the matrix of the second particle-matrix composite each have a cast microstructure.
 20. An earth-rotary drill bit comprising: bit body having a first region configured to carry one or more cutters for engaging a subterranean earth formation, the first region comprising a first particle-matrix composite material having a first material composition, and a plurality of regions configured for attachment to a drill string, the plurality of regions comprising a corresponding plurality of particle-matrix composite materials having a corresponding plurality of material compositions differing from the first material composition, each of the first particle-matrix composite materials and plurality of additional particle-matrix composite materials substantially formed of a plurality of hard particles dispersed throughout a matrix material, wherein the matrix of the first particle-matrix composite and the plurality of additional particle-matrix composites each have a cast microstructure, and a shank extending from at least one of the plurality of regions, the shank comprising an attachment portion configured to attach the shank to a drill string and a bit body portion for attaching the shank to a bit body.
 21. The rotary drill bit of claim 20, further comprising a steel blank having a lower portion that is metallurgically bonded to a plurality of the plurality of regions and an upper portion that is attached to the bit body portion of the shank. 